Research on Stability of PWM Controlled DC - DC Converters in CCM

Abstract

Stability is the intrinsic attribute of a system. A stable system may work well and effectively. For some PWM controlled converters, low frequency may occur in the output voltage and results in unsteadiness of the system. In this paper buck converters are taken as an example to investigate the stability feature. A delay in the feedback loop is related with stability closely, so the converter with a delay and without a delay are analyzed in detail, respectively. Differential equations for inductor current profile and output voltage profile are established. Characteristic equations are obtained from the differential equations. Based on Hurwitz Stability Criterion, stability requirement is derived from characteristic equations. It is shown that converters without a delay in the feedback loop are steady. On the other hand converters with a delay may be unsteady in some cases. Regulating parameters can avoid the low frequency ripple phenomenon. The proposed approach is verifieded by simulation. The simulation results show that the analysis is correct.